Fig. 5. In vitro temporal course of putative OREBP nuclear binding and D2 activity after hypo-osmotic challenge. To assess whether liver cells could detect and respond directly to osmotic changes, liver explants from seawater-adapted killifish were pooled and randomly distributed into iso-osmotic (control, C) or hypo-osmotic L-15 medium. (A) Temporal course of recruitment of putative OREBP into the nuclear compartment. Significant recruitment can be observed as early as 2 h after challenge and peaks at 4 h post-stress. The lower portion of A shows the quantification (relative intensity) of this response. (B) The associated increment in hepatic D2 activity (filled bars). Values are means ± s.e.m. of four separate experiments, each in triplicate. ^*P<0.05 vs control (open bars). Normalized D2 activity is expressed in arbitrary units (see Materials and methods).